1. Field of the Invention
The present invention relates to a system for monitoring slip the angle of a vehicle, such as an automotive vehicle. More specifically, the invention relates to a system which can project vehicular slip angle having simple construction and a simplified process.
2. Description of the Background Art
In modern control systems for controlling vehicular activity of an automotive vehicle, such as a suspension control system, an anti-akid brake control system, a power train control and so forth, the slip angle at a road wheel is one of the parameters for performing precise control operation. In order to monitor the wheel slip angle, Japanese Patent First (unexamined) Publication No. 62-299430 discloses a vehicular attitude control system for a four-wheel drive type vehicle, which controls wheel slip angle within a desired range. The disclosed system includes a longitudinal acceleration sensor for monitoring longitudinal acceleration exerted on the vehicular body and a lateral acceleration sensor for monitoring lateral acceleration exerted on the vehicle body. Wheel slippage data is derived by dividing the lateral acceleration value by the longitudinal acceleration value. The arithmetic operation is performed when a judgement is made that the vehicle is traveling on a curved road or corner. Such a judgement, in the proposed system, is made by monitoring steering angular displacement to detect a steering angle greater than a predetermined value. The disclosure further proposes to detect the vehicular condition of passing through the curved road or corner by comparing the longitudinal acceleration and the lateral acceleration.
The disclosed system intends to control the drifting magnitude of the four-wheel drive type vehicle for tight cornering and preventing spinning of the vehicle due to excess slip angle on the wheel. In this aspect, the disclosed system is successful for providing slip angle data for a control system which controls means for generating a yawing force for drifting.
However, when the disclosed system is applied for proving slip angle data for a purpose other than drift control, the accuracy level of detection of the occurrence of the lateral slip of the wheel simply monitored on the basis of the steering angle, cannot be satisfactorily high for a control operation requiring higher a precision level of detection of the slip angle. Namely, since the magnitude of lateral acceleration is variable depending upon the vehicle speed even at the same steering angular displacement, slip angle can be varied depending upon not only the steering angular position but also vehicular speed. When the vehicle speed is high, a relatively large wheel slip angle can be created even by a small magnitude steering angular displacement.
On the other hand, in the latter case, when the vehicle is driven at a substantially constant speed, the longitudinal acceleration on the vehicle body is maintained substantially zero. Therefore, any magnitude of lateral acceleration may cause the judgement that the vehicle is turning. Furthermore, when the vehicle is in deceleration (acceleration being negative), lateral acceleration held at zero becomes greater than the longitudinal acceleration to trigger slip angle derivation. On the other hand, while the vehicle is in a decelerating or acceleration state, the longitudinal acceleration can be greater than the lateral acceleration so that the system should ignote it so as to not perform derivation of the wheel slip angle despite the fact that the vehicle is turning.